1. Field of the Invention
A new improved catalyst system for alpha-olefin type polymerizations includes at least one organo metal compound having the formula R'''M in combination with a Group IVB-VIII transition metal compound on a support, at least one unhindered Lewis base and at least one hindered Lewis base wherein R''' is selected from the group consisting of C.sub.1 to C.sub.20 primary, secondary or tertiary alkyl, alkenyl or aralkyl groups, or a hydride, and M is selected from the group consisting of aluminum, gallium or indium. The improved catalyst system provides polymers having increased isotactic stereoregularity as well as lower catalyst residue.
2. Description of the Prior Art
There is extensive art on the polymerization of ethylene and higher alpha-olefins, including dienes, using Ziegler-type catalysts containing either alkyl metals or alkyl metals in which an alkyl groups has been replaced by X, OR", SR", NR".sub.2, etc., in combination with a transition metal compound of Groups IVB-VIII, where X=halide, and R"=C.sub.1 to C.sub.20 hydrocarbyl substituent.
It is well known to use various alkyl aluminum compounds in combination with transition metal compounds of Groups IVB-VIII in Ziegler-type polymerizations of alpha olefins. For stereospecific polymerization of propylene and higher alpha olefins, the most effective commercially used alkyl metal compounds are AlEt.sub.3 and AlEt.sub.2 Cl, although Al(n-Pr).sub.3, Al(n-Bu).sub.3, Al(i-Bu).sub.3 and Al(iBu).sub.2 H give similar results. Longer chain alkyl aluminums, such as Al(n-C.sub.6).sub.3, Al(n-C.sub.8).sub.3, (n-C.sub.8).sub.2 AlCl, etc., drastically reduce stereospecificity as shown by much lower heptane insolubles (Ziegler and Montecatini, Belgian Pat. No. 543,259).
This invention claims a novel catalyst system for stereospecific polymerization of propylene and higher alpha olefins to isotactic polymers. The new compositions include a Group IVB-VIII transition metal compound on a layer lattice support, at least one triorgano-metal compound of aluminum, gallium or indium, at least one unhindered Lewis base, and at least one hindered Lewis base. Higher activity and/or isospecificity is obtained than with the conventional di- or tri-alkyl metal compounds used in combination with the various types of supported transition metal catalysts, such as MgCl.sub.2 -supported TiCl.sub.4, supported TiCl.sub.3, etc., with or without other conventional catalyst modifiers present such as Lewis bases, alcohols, phenols, polymers, dispersants, binders and other additives.
A number of patents have been issued on the use of trialkyl metal compounds as cocatalyst for the polymerization of various monomers. These patents which are distinguishable from the instant invention are U.S. Pat. No. 3,953,414; Belgium Pat. No. 845,593; Belgium Pat. No. 846,314; German DT No. 2620-886; British Pat. No. 1,335,887; German DT No. 2630-585; British Pat. No. 1,140,659; German DT No. 2612-650; South African Pat. No. 7,503,470; German DT No. 2355-886; Japanese Pat. No. 51064-586; South African Pat. No. 7507-382; German DT No. 2638-429; Japanese Pat. No. 51057-789; U.S. Pat. No. 3,992,322; Japanese Pat. No. 52027-090; and U.S. Pat. No. 3,400,110.
Other patents which are distinguishable from the instant invention are U.S. Pat. No. 4,039,472; British Pat. No. 1,489,599; British Pat. No. 1,490,509; Japanese Pat. No. 1136-625; JA 7008 982-R; and Belgium Pat. No. 735,291.
It is also well known in the art to use various unhindered Lewis bases in combination with both unsupported and supported Ziegler-type catalysts to improve stereospecificity. Representative examples of such patents include U.S. Pat. No. 3,238,146; U.S. Pat. No. 4,107,413; British Pat. No. 1,001,820; U.S. Pat. No. 4,107,416; and German DT No. 2504-036.
These patents all fail to teach or suggest either the novel compositions or the improved polymerization results obtained with the compositions of this invention.